1. Field of the Invention
The present invention generally relates to information technology equipments and, more particularly, to a shield structure for information technology equipments, such as a notebook-type personal computer, provided with an opening for replacing a memory module.
2. Description of the Related Art
In recent years, it has become indispensable to take countermeasures against electromagnetic wave interference (EMI) or countermeasures against electrostatic discharge (ESD) with respect to information technology equipments such as a desktop-type personal computer (desktop PC), a notebook-type personal computer (note PC), a printer, a facsimile, etc. In EMC, especially, regulation for electromagnetic interference (EMI) has been progressed, and each country independently regulates its own standard or specification. Manufacturers of information technology equipments cannot sell or export their products unless they clear standards with respect to the EMI regulations. As standards with respect to the EMI regulations, there are, for example, Agreement of VCCI (Voluntary Control Council for Interference by Information Technology Equipment) in Japan, and the FCC rules and regulations in the United States.
As an international standard used as the basis of the rules regarding EMI regulations, there is a specification which is set by International Special Committee on Radio Interference (CISPR). It is the present status that each country establishes a specification based on the CISPR specification. Thus, if the CISPR specification is cleared, a rule of each country is almost cleared.
It is general in a note PC, which is one of information technology equipments, to apply a metal plate or a metal sheet or apply metal-plating on a backside of an enclosure so that electromagnetic waves do not leak from inside of the enclosure. By covering an entire surface of the enclosure, the equipment can have a structure in which electromagnetic wave do not leak outside. However, it is difficult to cover an entire surface of an enclosure. Especially, an opening part is formed on an enclosure at a portion provided with a connector for connection with external equipments, and electromagnetic waves may leak through the opening part.
Accordingly, as countermeasures against EMI, it is suggested to suppress such leakage of electromagnetic waves by attaching a metal made or metal-plated lid to an opening part of a shield structure and electrically connecting a metal portion of the lid to a ground potential portion of the enclosure (for example, refer to Patent Document 1).
Patent Document 1: Japanese Laid-Open Patent No. 2000-151132
In a personal computer or the like, in order to incorporate an expansion memory module into a printed circuit board inside an enclosure, usually, an opening for taking a memory module in and out is provided to the enclosure. The opening is closed by a metal made or metal-plated lid. However, it is difficult to completely cover a mating portion between a rim of the opening and an edge of the lid, and, thus, the EMI requirements may not be cleared due to leakage of electromagnetic waves from the mating portion.
Especially, in many cases in a note PC, a so-called butterfly type connection structure, which connects two memories to a connector part face-to-face, is used. According to the butterfly type connection structure, signal lines to the memories extend between the two memories. Since exchange of signals is performed frequently through the signal lines during operation of a CPU, the signal lines are source of generating electromagnetic waves.
Accordingly, if the butterfly type connection structure is used as an expandable and replaceable memory connection structure, there is a problem in that the EMI requirements cannot be cleared since an opening part of an enclosure is located near the butterfly type connection structure and leakage of electromagnetic waves through a periphery of the opening part become remarkable.
Moreover, an operation clock of CPUs is increased to a high frequency more and more, and with such an increase, an electromagnetic wave generated from the signal lines to the memories becomes a high-frequency. Thus, an electromagnetic wave tends to leak even through a small gap of shield.
Conventionally, if an amount of leakage of electromagnetic waves through an opening part for memory, a plurality of electromagnetic wave absorption sheet are applied to a lid, and, besides, an electrically conductive gasket or the like for electrically connecting a peripheral part of the lid and a periphery of the opening part is provided, as countermeasures against EMI. Such countermeasures against EMI requires costs of parts such as an electromagnetic wave absorption sheet and electrically conductive gasket and a process cost for operations to attach such a part, and, thus, there is a problem in that an increase in a manufacturing cost of a product itself is invited.